Fuses are frequently used to reconfigure memory and logic circuitry. For example, in dynamic or static memory chips, defective memory cells or circuitry may be replaced by blowing fuses associated with the defective circuitry while activating redundant circuitry to form new memory circuitry. This circuit rerouting using blowable fuse links contributes to enhanced yields without the necessity of scrapping defective process wafers.
Generally, fuse links, made of a conductive material, such as a metal may be blown or removed by passing an excessive current through the circuitry which melts the fuse link or exposing the fuse link to intense laser irradiation to ablate the fuse link including a window of thin transparent layer of oxide insulating material above the fuse link.
Frequently, it is more desirable to use the laser ablation method since it is faster, more accurate and leaves less residue within the fuse link window area. However, as device sizes decrease to 0.25 microns and below it is increasingly desirable and necessary to use multi-level device circuitry to achieve the desired circuit density. Low-K (low dielectric constant) materials have become necessary in the formation of dielectric insulating layers, also referred to as inter-metal or inter-level dielectric (ILD/IMD) layers in order to reduce capacitance and therefore speed signal transport. Low-K materials may include porous inorganic silicon oxide based materials such as carbon doped oxide also known by trade names such as BLACK DIAMOND™ and SILK™.
One problem with the use of low-K materials is the poor adhesive strength of such materials which are susceptible to delamination in the presence of induced stresses including thermal mismatch stresses. Guard rings have been proposed for use around fuse areas to prevent the migration of contamination from the fuse area into surrounding dielectric insulating areas following the ‘blowing’ of fuses to reconfigure the device circuitry.
For example U.S. Pat. No. 5,729,041 (Yoo et al.) describes a structure and method of forming a fuse link and fuse window area having a protective layer formed over them. The protective layer is highly transmissive to intense laser light while it is protective of the fuse and the surrounding insulating layers.
U.S. Pat. No. 5,567,643 (Lee et al.) describes a method for creating a guard ring surrounding a fuse area. The guard ring prevents contaminants from diffusing through a window opening above a fuse link to adjacent semiconductor devises. The guard ring is an annular metal ring that penetrates two or more insulating layers.
U.S. Pat. No. 6,319,758 (Liaw et al.) describes a method for forming a fuse area including use of a hard mask to facilitate destruction of a conductive fuse link.
U.S. Pat. No. 6,295,721 (Tsai et al.) describes a method for forming a fuse link from a compound layer of aluminum and chromium. The fuse link is shaped to form a stripe that bridges a gap between two copper dual damascene connectors. By controlling the degree of overlap between the stripe and the connectors, the conductance of heat from the stripe into the connectors can be varied, thereby allowing control of the manner in which the fuse blows when subjected to heating.
U.S. Pat. No. 6,100,118 (Shih et al.) describes a method and structure for forming a multi-layer guard ring structure around a fuse area that extends through multiple dielectric layers to an upper metallization layer.
One problem not addressed or solved by the prior art including the above cited references is the problem of damage including delamination to low-K dielectric insulating layers underlying the fuse link during the laser ablation or current heating process to blow the fuse links.
Therefore, there is a need in the semiconductor processing art to provide a structure and method of forming fuses such that the fuse link portions of a fuse may be removed while avoiding damage to underlying dielectric insulating layers.
It is therefore an object of the invention to provide a structure and method of forming fuses such that the fuse link portions of a fuse may be removed while avoiding damage to underlying dielectric insulating layers in addition to overcoming other shortcomings of the prior art.